In situ unveiling the conversion processes on the catalytic cathode in lithium-sulfur batteries.

Lithium-sulfur (Li-S) batteries have attracted attention due to their high theoretical capacity of 1675 mAh g-1. However, a knowledge gap remains regarding nanoscale lithium sulfide (Li2S) reactions, limiting full S utilization and rational catalyst design. Here, we show how Li2S nanoclusters transform and distribute under operation using in situ atomic force microscopy, providing the structure-(re)activity relationships. Comparing to the lamellar structures formed at noncatalyzed electrodes, Li2S deposited at Pt catalytic electrode exhibited a spherical morphology. The zero-order reaction kinetics was captured on catalytic surfaces, differing from noncatalyzed electrodes. The electrodeposition of Li2S follows the overpotential-driven progressive and instantaneous nucleation processes, showing a promoted deposition and reversible dissolution at the overpotential of 80 mV. The Li2S transformation under high polysulfides concentrations indicated that an increase of catalytic sites and uniform distribution of Li2S would be critical for practical Li-S batteries. Our work provides fundamental insights into Li2S reaction kinetics, advancing the development of energy storage systems.